It is indeed the technique on the post-it paper, although I did the pattern with normal paper.

I had a question for you, would you want to swap ATC-cards with me? We’re having an exposition and we’re trying to get as much ATC-cards as possible, to create a wall of ATC-cards. We’re working around the theme: ‘Travel around the world’ and we’re trying to get ATC-cards from all around the world to put on the wall. We don’t have any yet of Portugal :-) And if you know some people who want to trade, it would be a great help! :-)